The major findings suggest that there is a copper protein which can transfer electrons from sodium dithionite to proline reductase during the reduction of D-proline. Additional electron transport protein(s) are involved in coupling NADH to the terminal portion of this reduction system. BIBLIOGRAPHIC REFERENCES: T.C. Stadtman, J.E. Cone, R. Martin del Rio, J.B. Jones and B. Seto. Selenoenzymes of Bacteria. Proc. of Symp. on Selenium-Tellurium in the Environment. Univ. of Notre Dame, Notre Dame, Ind. p. 226-233 (1977). Belinda Seto and T.C. Stadtman. Purification and Properties of Proline Reductase from Clostridium sticklandii. J. Biol. Chem. 251, 2435-2439, (1976).